For example, a radar device or the like having a phased array antenna mounted thereon needs to be equipped with a shifter that is capable of shifting a phase of a high frequency signal in order to vary a beam direction.
As the shifter capable of shifting a phase of a high frequency signal, a vector sum phase shifter is known.
The vector sum phase shifter typically includes: an orthogonal signal generator for generating from a high frequency signal an in-phase (I) signal and a quadrature (Q) signal orthogonal to each other; a first variable gain amplifier for amplifying the I signal generated by the orthogonal signal generator; a second variable gain amplifier for amplifying the Q signal generated by the orthogonal signal generator; and a signal combiner for combining the I signal amplified by the first variable gain amplifier and the Q signal amplified by the second variable gain amplifier, and for outputting a combined signal for the I signal and the Q signal.
In addition, the vector sum phase shifter includes: a table memory for storing a relation between the phase shift amount and gains of the first and second variable gain amplifiers; and a gain controller for acquiring gains associated with a phase shift amount provided from an outside by reference to the table, and for applying the acquired gains to the first and second variable gain amplifiers.
In the vector sum phase shifter with high phase shift precision, the phase difference between the I signal and the Q signal generated by the orthogonal signal generator is not shifted from 90°, and thereby the orthogonality between the I signal and the Q signal is kept. Further, the I and Q signals uniformly have the same amplitude.
The orthogonal signal generator is typically realized by an RC polyphase filter consisting of a resistor and a capacitor. However, for example, in a case where a quadrature error and an amplitude error of the I signal and the Q signal occur due to an influence of manufacturing variation of the RC polyphase filter, the phase shift precision is decreased, and thus the influence of manufacturing variation needs to be eliminated.
Non-Patent Literature 1 mentioned below discloses a calibration method of eliminating the influence of manufacturing variation by preparing a plurality of varactors usable as the capacitance of the RC polyphase filter, and selecting one of the prepared varactors to be used for the RC polyphase filter in dependence on the quadrature error and the amplitude error of the I signal and the Q signal.